1. Field of the Invention
The invention relates to a method and apparatus for removing unwanted biological tissue. It relates more particularly to surgery using an endoscopic ultrasonic aspirator with an elongated hollow probe and simultaneous irrigation and aspiration, which disintegrates and removes highly compliant tissue from deep within the body through a narrow surgical orifice.
2. Description of Related Art
The endoscopic ultrasonic aspirator (hereinafter "EUA") of the present invention is particularly useful in the field of transurethral resection (TUR) of the prostate gland or other urological surgery, including destruction and removal of bladder stones. More generally, it is useful in any type of surgery in which deep penetration of the body through a narrow orifice is required, for example arthroscopic surgery, diskectomy, or other orthopedic surgery.
In a preferred embodiment of the invention, an ultrasonic probe with a high peak tip velocity is insertable at least about 19 cm into the body for disintegrating compliant tissues, simultaneously irrigating the operating site, and aspirating fluid and tissue, through a surgical orifice no more than about 29 mm in circumference, which is the accepted maximum dimension for an instrument to be inserted into the urethra. The circumference of the instrument may be as great as about 29 mm, but preferably is no more than about 25 mm.
A unit of measurement known as the French is frequently used to denote circumferential size. A sheath size in French is three times the sheath's diameter in millimeters. Thus, a sheath having a circumference of 30 mm has a diameter of 30/.pi.=9.55 and a French size of 9.55.times.3=28.65.
Since the 1950's TUR has been the procedure of choice for removal of the diseased prostate gland. In one conventional procedure, the patient is placed in the conventional lithotomy position under spinal anesthesia. An elongated resectoscope with a light source, a telescope, a cutting electrode, and a source of continuous irrigation is inserted into the urethra and advanced to the vicinity of the prostate gland, where access to the prostate is gained through the urethral wall. The cutting electrode is a semicircular wire mounted at the end of a slidable shaft for antegrade and retrograde motion; that is, toward the front and rear of the patient. The electrode is supplied with a pulsed RF current which both cuts and cauterizes tissue. The shaft is spring-biased toward the rear of the patient and is repetitively drawn forward by a trigger-like lever as the electrode slices off small slivers of prostate tissue.
As the tissue is sliced off it is washed into the bladder by the continuous irrigation, which fills the bladder about every 5 minutes. The accumulated water and debris must be removed periodically with a suction device such as the Ellik evacuator, which has a squeeze bulb coupled to a flexible plastic catheter. The resectoscope is removed, the bulb is compressed and the plastic catheter is inserted to the operative site. Then the bulb is expanded to draw out the water and tissue debris.
This traditional procedure has a number of disadvantages that the present invention is intended to avoid. In order for the surgeon to view the operating site, the EUA must be provided with some type of viewing and lighting system. It has been found that, at the present level of optical technology, an adequate endoscopic view of surgical procedures requires an optical relay lens system that uses lenses with a diameter of about 2.5 mm. Since these lenses must be mounted within a rigid tube that also contains illumination fibers, the total diameter of the finished telescope typically measures about 4 mm. Additionally, in order for a hollow ultrasonic tip to remove firm prostatic tissue at an adequate rate (typically from about 5 to about 10 grams per minute), the bore of the tip must also be about 4 mm.
In an endoscopic aspirator, both the telescope and the tip are placed side by side within a sheath. When the endoscopic aspirator is inserted into a patient's body, the sheath protects the surrounding tissue from contacting the ultrasonic tip which vibrates not only at its surgical extremity but also along its entire length.
The use of a loop-shaped electrode for cutting requires antegrade cutting so that removed tissue does not build up in front of the loop and block the viewing lens. However, with antegrade cutting, the loop is always hidden under some thickness of tissue. This leads to the risk that the surgeon's view will be blocked and the urinary sphincter, the bladder wall, or even the intestines may be accidentally damaged. The surgeon can also pierce the prostate capsule, which is the tougher outer skin of the prostate, and injure the blood vessels beyond. Electrical cutting is very fast, so these can occur even with the exercise of due care. Further when the telescope of the EUA is positioned adjacent to the ultrasonic tip, the walls of the ultrasonic tip interfere with the surgeon's view of the operating site.
Also, evacuation must be performed 10 to 20 times, removing the resectoscope each time, and this may take up as much as 20 to 50 percent of the one-hour operating time.
Another disadvantage of the prior procedure is that the continuous irrigation flow described above causes filling and distention of the bladder and absorption of the fluid into the blood, leading to the danger of hypervolemia or hyponatremia. Also, electrical cutting requires the use of a relatively expensive non-conducting fluid medium such as isotonic glycine. If a conducting fluid such as saline is used, the cutting current can be short-circuited away from the work. The fluid must be isotonic to avoid intravascular hemolysis.
Further, the prior procedure is incapable of removing bladder stones, which may necessitate two operations where a single operation would have been preferable.
Since the EUA is frequently used in the field of transurethral resection, the EUA must frequently be inserted into the urethra. Therefore, the circumferential size of the sheath of the EUA is limited by the elastic extension of the urethra which is typically about 30 mm (or about 28 French). Surgeons, however, prefer to use sheaths of smaller size, such as 24 or 25 French, to avoid the occurrence of strictures or contractions of the urethra following excessive endoscopic dilation.
Endoscopic ultrasonic tissue removal and aspiration avoids these disadvant ages. Ultrasonic tissue removal has been employed in the past for dissection and removal of biological tissue. However, no ultrasonic instrument has been available to remove highly compliant tissues through a narrow orifice, for example in transurethral prostate resection. The prior art has two principal failings. First, there was no long, slender probe capable of sustaining ultrasonic vibrations at the high tip velocities that are necessary for removal of such tissues. Second, the art has not realized that the most efficient tissue removal is by ultrasonic vibrations causing cavitation of the fluid within the cells. Such vibrations should preferably be in the 10-20 kHz range, although other frequencies may be used. The term "ultrasonic" will be employed herein to refer to all the frequencies of interest, including some frequencies in the audible range.
In one early development, Von Ardenne and Grossman reported in 1960 on the use of ultrasonic vibration to assist in inserting small-gauge wire probes and hollow needles into the skin. They mention constructing an ultrasonically vibrating needle connected to a syringe which is adapted to inject or withdraw fluid or other material from adjacent the tip of the needle. They employ a velocity transformer of the exponential type and operate at a frequency of about 25 kHz with a tip excursion of about 10-100 microns.
Also in 1960, Watkins et al. reported the use of an ultrasonic chisel to fracture and remove calcium deposits from cardiac valves. The authors state that their technique is unusable on soft, flexible tissues since the belief at the time was that such tissues are relatively undisturbed by ultrasonic vibration. Their apparatus operates at about 26.5 kHz with a tip excursion of about 38 microns.
Ultrasonic energy has also been employed to cavitate a liquid medium to burst and destroy suspended microorganisms for either sterilization or extraction of the protoplasm. This technique typically employs a solid round metal horn immersed in the liquid medium and vibrating at perhaps 20 kHz with a stroke of about 20-40 microns. It operates by cavitating the water around the cells, rather than the intracellular water.
Prior patents have disclosed surgical instruments in which ultrasonically vibrating tools remove unwanted biological material while providing irrigation of the work area and aspiration of fluids and removed material. See, for example, U.S. Pat. No. 2,874,470 to Richards, U.S. Pat. No. 3,526,219 to Balamuth, U.S. Pat. No. 3,589,363 to Banko and Kelman, and U.S. Pat. No. 4,063,557 to Wuchinich et al. The Richards device is a dental instrument which operates above the audible range, preferably at about 25 kHz, with an amplitude of about 10 microns. In the Balamuth '219 device, a sharp-edged tool vibrating at about 25 kHz directly contacts tissue to "chop" it. In the Banko and Kelman '363 device, a thin-walled tubular tip which vibrates with an amplitude of about 50-70 microns breaks apart and removes relatively hard biological material such as cataract material in the lens of the human eye. The Wuchinich et al. '557 patent discloses a device for removing compliant tissues such as neurological neoplasms, employing a magnetostrictive transducer which vibrates at about 25 kHz with a stroke of about 25 microns. A stepped and tapered mechanical transformer increases the stroke to about 125-400 microns.
None of these devices has been capable of providing sufficient tip velocity and a long and narrow enough probe to perform endoscopic surgery. The greatest insertable distance available with prior ultrasonic surgical instruments has been about 7-8 cm. More particularly, prior devices have been unable to exert sufficient sound pressure on compliant cells in a biological tissue structure such as a glandular tumor to produce cavitation in the intracellular fluids of the cells, or to disintegrate them in any fashion.